1. Technical Field
The present invention relates to a hydrodynamic bearing device that is mounted in a hard disk drive apparatus or the like, and to a spindle motor that is equipped with this hydrodynamic bearing device.
2. Description of the Prior Art
Hydrodynamic bearing devices having hydrodynamic bearings that afford lower NRRO (non-repetitive runout) and are quieter because of non-contact rotation have been mainly used in recent years in hard disk drives (hereinafter referred to as HDDs) and other such disk driving apparatus.
With hydrodynamic bearing devices such as this, it is preferable to employ a configuration in which as much length as possible is ensured for the radial bearing portion formed in the gap between the shaft and the sleeve in order to increase the angular stiffness (or moment stiffness) of the hydrodynamic bearing. Meanwhile, because of the need to reduce the thickness of a spindle motor, the configuration has to be such that the radial bearing portion is long enough, while the thickness of the hydrodynamic bearing device does not increase. The “angular stiffness” here refers to the degree to which axial tilt caused by disturbance during operation is restored.
For example, Patent Document 1 (Japanese Laid-Open Patent Application 2008-43197) discloses a motor in which a flange-like plate fixed to a shaft is provided on the inner peripheral surface side of a sleeve cap, a boss is provided under a hub, and a seal is formed in the gap between the sleeve cap and the plate. With this configuration, the presence of a lubricant between the sleeve cap and the plate evens out the internal pressure and increases stability, and allows a better sealing effect to be obtained.